OF THE SPOTS ON THE MOON.

Others say that the moon is composed of more or less transparent
parts; as though one part were something like alabaster and others
like crystal or glass. It would follow from this that the sun
casting its rays on the less transparent portions, the light would
remain on the surface, and so the denser part would be illuminated,
and the transparent portions would display the shadow of their
darker depths; and this is their account of the structure and nature
of the moon. And this opinion has found favour with many
philosophers, and particularly with Aristotle, and yet it is a false
view--for, in the various phases and frequent changes of the moon
and sun to our eyes, we should see these spots vary, at one time
looking dark and at another light: they would be dark when the sun
is in the West and the moon in the middle of the sky; for then the
transparent hollows would be in shadow as far as the tops of the
edges of those transparent hollows, because the sun could not then
fling his rays into the mouth of the hollows, which however, at full
moon, would be seen in bright light, at which time the moon is in
the East and faces the sun in the West; then the sun would
illuminate even the lowest depths of these transparent places and
thus, as there would be no shadows cast, the moon at these times
would not show us the spots in question; and so it would be, now
more and now less, according to the changes in the position of the
sun to the moon, and of the moon to our eyes, as I have said above.